Catalysts containing vanadium as a principal component have been studied or industrially used in various reactions, such as synthesis of phthalic anhydride by the oxidation of o-xylene or naphthalene, synthesis of pyromellitic dianhydride by the oxidation of durene, synthesis of maleic anhydride by the oxidation of benzene or n-butane, synthesis of benzonitrile by the ammoxydation of toluene, synthesis of substituted benzaldehyde by the oxidation of substituted toluene, synthesis of acrylic acid by the oxidation of acrolein, synthesis of formaldehyde by the oxidative dehydrogenation of methanol, synthesis of propylene and butenes by the oxidative dehydrogenation of propane and butanes, synthesis of acrylonitrile and methacrylonitrile by the ammoxydation of propane and isobutane, synthesis of sulfuric acid by the oxidation of SO.sub.2, reductive denitration of nitrogen oxide by means of ammonia, and decompositions reaction of organic halides.
In the above-mentioned conventional catalysts, vanadium presents in the form of oxide or composite oxide with other component. Vanadium is often used as a molded catalyst prepared by molding such oxide or composite oxide, or a supported catalyst containing such oxide or composite oxide supported on a carrier. The preparation of such a catalyst has been carried out by using an aqueous solution of water-soluble salt like ammonium metavanadate and vanadyl oxalate, or an aqueous solution obtained by dissolving such a water-soluble salt or vanadium pentoxide in an oxalic acid and a mineral acid such as hydrochloric acid; impregnating a carrier with the solution, or mixing the solution with other component.
However, since the conventional vanadium-containing catalysts are formed by only compulsory deposition of a vanadium component on a carrier or solidifying a vanadium component, for example, by evaporating and drying a solution containing vanadium component, and therefore the interaction with the carrier or other component is weak. Hence, non-uniformity of supported component and nonhomogeneous mixing are unavoidable due to the movement of substances during drying. Thus, the conventional vanadium-containing catalysts cannot achieve sufficient catalytic performance because of poor dispersion, uniformity and thermal stability of an active catalyst component having catalytic activity, insufficient reaction yield and catalyst life.
For example, phthalic anhydride is synthesized by the oxidation of o-xylene using a catalyst system for which V.sub.2 O.sub.5 --TiO.sub.2 are essential. In this case, in ideal, the use of a catalyst system having a monolayer of V.sub.2 O.sub.5 on the surface of anatase type titania is preferred. However, in the conventional process for manufacturing catalysts, it is difficult to achieve such an ideal dispersion state.
A reductive denitration of NO.sub.x is performed by NH.sub.3 over the catalyst system containing V.sub.2 O.sub.5 --TiO.sub.2. However, in this case, the catalyst obtained by the conventional manufacturing process also faces a limitation in its thermal stability. Namely, such a catalyst can be used in a low-temperature range, but cannot be used in a high-temperature range exceeding 500.degree. C.
For example, it is known that a catalyst system containing V-Mg composite oxide is effective for the oxidative dehydrogenation of propane and butanes. In a prior art, an effective phase formation is performed by calcining the solid phase at high temperatures in the final stage. However, like the above-mentioned case, the control of the phase formation is extremely difficult due to the non-uniformity of mixing of components. Thus, this catalyst system has not reached an industrially implementable level.
Moreover, in the conventional process for manufacturing a vanadium-containing catalyst, calcination at high temperatures is essential to remove residues like residues of vanadates and organic substances used as starting materials, thereby restricting the preparation conditions of catalysts. Consequently, the performance of the catalysts is limited.
As special preparation methods, a sol-gel method using vanadyl alkoxide, a liquid-phase deposition method using VOCl.sub.3, and a CVD (Chemical Vapor Deposition) method are listed. However, these methods require expensive starting materials or a special device, and are not suitable for mass-production. Hence, these methods have not been put to practical use.
Hence, vanadium-containing catalysts that achieve excellent dispersion, uniformity and thermal stability and high catalytic performance are required for various reactions. The present invention was implemented to solve the above-mentioned conventional problems, and its object is to provide novel vanadium-containing catalysts achieving excellent dispersion, uniformity and thermal stability, and high catalytic performance for various reactions. It is another object of the present invention to provide a process for manufacturing a vanadium-containing catalyst achieving excellent dispersion, uniformity and thermal stability, and high catalytic performance. It is still another object of the present invention to provide a process for efficiently manufacturing phthalic anhydride, isobutene, methyl formate, benzaldehyde, benzoic acid, anisaldehyde, propylene, or acrylonitrile by means of a vanadium-containing catalyst.